More than seven hundred million golf balls are produced each year, a significant percentage of which have indicia or logos printed on their outer surface. The indicia typically include any one of the golf ball company, trade name, a number, or an image, such as a corporate or country club logo. The indicia are typically printed on a base-coated surface of the cover of the golf ball, and covered with a top-coating to prevent damage during impact with a golf club. Thus, the indicia must have a perfect appearance since it is often the most distinctive quality of a golf ball.
The golf ball cover typically contains a white or other colored concentrate, or is painted. The most common method for adding a logo to the dimpled surface of a golf ball is by pad printing, although other methods, such as inkjet printing, are adaptable for such surfaces. However, whatever method is used the golf ball must be first, oriented for the printing step(s), secondly, they must be printed on at least three sides, preferably four, and finally, there must be a method of inspection for those golf balls, which during the process have a flaw or defect in the printing.
There has been a continuing desire to achieve high production rates. Because automated apparatus typically may function faster than human operators, there has been an ongoing goal to reduce, if not eliminate, human intervention during the manufacturing process. Thus, each of the above processes is typically done at a separate automated processing station functioning at optimal efficiency and speed so that the overall production rate is maintained at the desired high level. For instance, pad-printing apparatus preferably includes an array of print-pads arranged to apply a production print sequentially on various locations on the surface of the golf ball, the golf ball being indexed before being passed to the next print-pad.
The pad printing process begins by spreading ink across the surface of a pad printing cliche or “plate” containing etched or depressed version of the desired image. Ink is dispersed over the etched area and excess ink is removed with a “doctor” blade or cup. Upon exposure to air, thinner evaporates from the ink causing it's surface to become “tacky.” A smooth, resilient, block of silicone rubber (the “pad”) is brought into contact with the tacky surface of the ink. As the pad is withdrawn from the plate surface, an adhering film of ink is transferred to the pad. The ink is carried on the pad to the target area on the golf ball surface, during which time thinner in the ink further evaporates, causing the exposed ink surface on the pad to become tacky. Upon contact with the golf ball surface, the film of ink is transferred from the pad to the ball surface.
Pad printing plates are typically stiff plates coated with a photopolymer material that cures upon exposure to UV light. The etched version of the image is formed by placing a film positive of the image over the plate and irradiating the surface with UV light. In this manner, the exposed areas of the plate harden, while blocked areas remain soft. The soft polymer is then removed by a series of washing steps, creating etched areas correlating to the logo.
While the golf industry needs improvement in automatically orienting, printing and inspecting golf balls produced by high speed production lines, the challenge is in the indexing of the golf ball such that multiple surfaces of the ball are presented sequentially and with extreme precision to the pad printers for the printing of indicia without interrupting the production cycle. This requires accurate indexing of the ball and the maintaining of that index.